1. Technical Field of the Invention
The invention relates to an emergency terminal speed limiting device for an elevator and, more particularly, to improvements in the detection of position checkpoints in terminal zones of the elevator hoistway.
2. Discussion of Related Art
It is known in the elevator art to define terminal zones at both ends of the elevator hoistway. It is desired that the elevator car stop normally at a top or bottom landing of the hoistway in such a terminal zone. In the event the elevator car enters a terminal zone, it is necessary to provide a primary means for controlling the elevator car as well as one or more backup means. One such backup means is called emergency terminal speed limiting. For checking the position of the car, conventional emergency terminal speed limiting devices use vanes mounted in the terminal zones of the hoistway. The vanes act as cams used to actuate switches that are mounted on the elevator car. Each switch has an arm attached to a roller that rolls along the cam as the car passes by the cam thereby actuating the switch. Since the terminal zone is often on the order of twenty-five meters or more in length, these vanes are quite long. Consequently, transport of these vanes from factory to hoistway is difficult, not to mention difficulties in their installation. Since one sensor track is used for each of the position checkpoints, one vane is used for each such position checkpoint in each terminal zone. As a result, there is a great deal of material and manpower used for the installation of these vanes and there is one switch needed for each vane.